look at the center turbine just b4 the blade hit the tower it flexed and that is what caused the blade to hit the tower. there was a major malfunction in one of the blades causing an unbalance which threw the blades into the tower.

It appears one of the blades came apart first, the unbalanced mass flexed the tower enough for one of the other blades to impact the tower. You can see the explosion of the blade as the crease in the tower in created. I understand that these windmills are to turn at the same rpm no matter the wind speed. This is acomplished by changing the pitch of the blades. The ability to change the pitch must be what failed and caused it to overspeed.

It is obvious that we can no more explain a passion to a person who has never experienced it than we can explain light to the blind. T.S.Eliot

It makes sense that the blade actually broke. Not only is it subject to extreme centrifugal force from over-speed, but the wind is probably not constant, so the blade is flapping back and forth (out of the plane of the three blades) with the gusts.